One of my head bolt holes has some damaged threads and is probably going to need repairing. Can I Helicoil this with the engine in the car? I'm concerned about the metal chips/savings from drilling the hole going into the coolant jacket. Has anyone actually done this in-situ? On a scale of 1-10 (1 being easiest), how difficult is it to perform the procedure? I've seen some YouTube clips and it seems (deceptively?) easy. Am I right in thinking the Helicoil insert will allow me to use the original (OE) head bolts? Are the threads UNC or UNF?

Installing a helicoil doesn't involve a high degree of difficulty; but I would be hesitant on using them in that application......high amount of torque on the head bolt and the fear of the helicoil breaking or pulling out would make me nervous. I'm not saying it should never be done.......just not my cup of tea.

Short of welding it up and risking warpage from the heat, a helicoil is about the best option.

If it were me, I'd do the helicoil- use grease on the drill bit and tap to catch as much of the filings as you can- and use a stud in that hole. This will put less stress on the threads and I'll bet you'll be fine.

Short of welding it up and risking warpage from the heat, a helicoil is about the best option.

If it were me, I'd do the helicoil- use grease on the drill bit and tap to catch as much of the filings as you can- and use a stud in that hole. This will put less stress on the threads and I'll bet you'll be fine.

Yep,,,,,,,,yep,,,,,,,,,and you betcha!!

Helicoils are a great invention and without being able to totally prove the following statement, i'll still venture that there are millions of engines out there with helicoiled head bolts doing a fine job. Go for it, it's easier than it looks! LOL Buy the "kit" for the head bolt size. It comes with the correct size drill bit and about 6 coils so you end up with the correct size threads to match the head bolts.

The helicoil will be stronger than the original thread, no worries there.

I would drill out a piece of scrap steel or aluminum to guide the tap and drill that you can clamp down to the block to make sure its perfectly straight. If you tape off the exposed holes and use a shop vac to get all the chips/shavings you should have no problems.

A small flat on the face of the drill giving a small negative rake zone will prevent digging in when you are enlarging the bolt hole to tap drill size for the helicoil.

For the cost of a helicoil kit and the work involved you might consider taking it to a good machine shop, they should have the tools already and the experience to make it painfree.

Thanks for all the info guys. I've arranged a guy from my local machine shop to come out tomorrow and do the helicoil. He doesn't normally do mobile stuff (too much hassle, he says) but, as we know each other quite well now, he said he'll make an exception. He seems confident and I'm thankful the bolt hole is one of the short ones so it will be a LITTLE less critical to keep the drill 100% straight.

have him check with machine shop tool and equipment supply(R.L. stephens anahiem ca) for threaded insert.
1 piece- threads on inside & outside if you have the room,
it is much stronger & won't back out

Just to update this and close it off, the machine shop guy came out this afternoon and helicoiled the bolt hole no problem. Hardest part seemed to be 1) drilling the hole (drill kept jamming-up... he took it very slow and steady) and 2) getting the tap started. He drilled the hole free-hand. He used 2 old head bolts in the holes either side of the hole to be drilled to use as a visual reference point and I knelt-down at the front of the car to tell him if it all looked straight from that angle. If there's a next time, I think I'll do it myself... pretty straightforward stuff if you're careful.

Glad it worked out for you. Sorry I didn`t see this post sooner as I would have advised you the same as 4 Jaw Chuck. Many professional racers will heli coil every cylinder head bolt hole as they are way stronger than the stock cast iron threads.

Glad it worked out for you. Sorry I didn`t see this post sooner as I would have advised you the same as 4 Jaw Chuck. Many professional racers will heli coil every cylinder head bolt hole as they are way stronger than the stock cast iron threads.

You know, that did occur to me and I actually commented to the guy that did the job that, if I was building-up a seasoned block, I would address all of the head bolt holes along with all the other machining work; for the time and cost involved, it would seem to be a no-brainer really.

Glad it worked out for you. Sorry I didn`t see this post sooner as I would have advised you the same as 4 Jaw Chuck. Many professional racers will heli coil every cylinder head bolt hole as they are way stronger than the stock cast iron threads.

Hi there, i have the same problem and the thing is, the advised of 4 jaw chuck doesn't work on me. Can you gave me another advise here, or maybe i just did something wrong? I really don't know what to do.

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